The present invention relates to chemical compounds which have an ionic structure and in combination with an organometallic transition metal compound form a catalyst system which can advantageously be used for the polymerization of olefins.
Ziegler-type catalysts based on angled metallocenes of metals of group IV form a new generation of industrially usable catalysts for the polymerization of xcex1-olefins (H. H. Brintzinger, D. Fischer, R. Mxc3xclhaupt, R. Rieger, R. Waymouth, Angew. Chem. 1995, 107,1255-1283).
To obtain an active catalyst system, the metallocene complex is treated with a large excess of methylaluminoxane (MAO) (H. Sinn, W. Kaminsky, Adv. Organomet. Chem., 1980, 18, 99). Apart from the high cocatalyst costs, this has the disadvantage of a high aluminum content in the polymer obtained. For this reason, new activation methods which make do without superstoichiometric amounts of activator have been developed.
The synthesis of xe2x80x9ccation-likexe2x80x9d metallocene polymerization catalysts is described in J. Am. Chem. Soc. 1991, 113, 3623. Here, the alkyl group is abstracted from an alkyl-metallocene compound by means of trispentafluorophenylborane which is used in a stoichiometric amount relative to the metallocene.
EP-A-0,427,697 claims this synthetic principle and a corresponding catalyst system comprising an uncharged metallocene species (e.g. Cp2ZrMe2), a Lewis acid (e.g. B(C6F5)3) and aluminum alkyls. A process for preparing salts of the formula LMX+XAxe2x88x92 according to the above-described principle is claimed in EP-A-0,520,732.
EP-A-0,558,158 describes zwitterionic catalyst systems which are prepared from dialkyl-metallocene compounds and salts of the formula [R3NH]+[BPh4]xe2x88x92. The reaction of such a salt with, for example, Cp2*ZrMe2 results in protolysis with elimination of methane to give a methyl-zirconocene cation as an intermediate. This reacts via Cxe2x80x94H activation to give the zwitterion Cp2*Zr+-(m-C6H4)-BPh3xe2x88x92. Here, the Zr atom is covalently bound to a carbon atom of the phenyl ring and is stablilized by means of an agostic hydrogen bond.
U.S. Pat. No. 5,348,299 claims corresponding systems in which dimethylanilinium salts with perfluorinated tetraphenylborates are used. Apart from the activating action of the borate salts, their ligand sphere excercises an important influence on the reaction equilibrium. Large bulky ligands largely prevent the dimerization of the metallocenium fragments and thus displace the equilibrium to the side of the catalytically active species. The previously described mononuclear borate anions have four aryl ligands and can, as a result of the incorporation of bulky groups on the ligand, exercise an influence on the reaction equilibrium (WO 95/24268). Disadvantages of these systems are the complicated syntheses, and also the extreme sensitivity of the resulting metallocenium complexes.
It is an object of the present invention to provide a chemical compound having a novel ligand system which retains the advantages of bulky ligands but does not have the disadvanatages of the existing bulky aryl ligands.
We have found that this object is achieved by a chemical compound of the formula I,
[M1Qx1Qy2Qz3]xe2x8ax96Axcex2xe2x80x83xe2x80x83(I)
where
M1 is an element of group IIa, IIa, IVa or Va of the Periodic Table of the Elements,
x is 0 or 1,
y is 0 or 1 and
z is 0 or 1 and
A is a cation of group Ia, IIa, IIIa of the Periodic Table of the Elements, a carbenium, oxonium, phosphonium or sulfonium cation or a quaternary ammonium compound, and
Q is a ligand system based on a biphenyl skeleton which is bound to M1 via the positions 2 and 12 and has the formula (II) 
xe2x80x83where
R1, R2, R3, R4, R5, R6, R7 and R8 are identical or different and are each a hydrogen atom, a halogen atom, a C1-C40 group such as C1-C20-alkyl, C1-C20-haloalkyl, C1-C10-alkoxy, C6-C40-aryl, C6-C40-haloaryl, C6-C40-aryloxy, C7-C40-arylalkyl, C7-C40-haloarylalkyl or C7-C40-haloalkylaryl, or an OSiR39 group, where R9 are identical or different and are each a hydrogen atom, a halogen atom or a C1-C40 group such as C1-C20-alkyl, C1-C20-haloalkyl, C1-C10-alkoxy, C6-C40-aryl, C6-C40-haloaryl, C6-C40-aryloxy, C7-C40-arylalkyl, C7-C40-haloarylalkyl or C7-C40-haloalkylaryl. Furthermore, two or more radicals R1 to R8 may be connected to one another in such a way that they form a monocyclic or polycyclic ring system which may in turn be substituted.
Preference is given to compounds in which M1 is boron and which have the formula (III),
[BQ1Q2]xe2x8ax96A⊕xe2x80x83xe2x80x83(III)
where
A is a cation of group la, lha, Ilia of the Periodic Table of the Elements, a carbenium, oxonium, phosphonium or sulfonium cation or a quaternary ammonium compound,
Q1 and Q2 may be identical or different and are each a ligand system based on a biphenyl skeleton which is bound to B via the positions 2 and 12, where Q corresponds to the groups indicated under the formula (II).
Preference is likewise given to compounds in which M1 is phosphorus and which have the formula (IV),
[PQ1Q2Q3]xe2x8ax96A⊕xe2x80x83xe2x80x83(IV)
where
A is a cation of group Ia, IIa, IIIa of the Periodic Table of the Elements, a carbenium, oxonium, phosphonium or sulfonium cation or a quaternary ammonium compound,
Q1, Q2, Q3 are identical or different and are each a ligand system based on a biphenyl skeleton which is bound to P via the positions 2 and 12, where Q is as defined for the formula (II).
Particularly preferred but nonlimiting examples of the novel chemical compound of the formulae (III) or (IV) are: 
A novel chemical compound of the formula (I) can be prepared, for example, according to the following reaction scheme: 
where
Bs is a base, preferably an element of group Ia or IIa of the Periodic Table of the Elements or an organolithium compound or a Grignard compound,
X independently of one another are identical or different and are each a leaving group, preferably a hydrogen or halogen atom,
Y independently of one another are identical or different and are each a leaving group, preferably a hydrogen or halogen atom,
M1 is an element of group IIa, IIIa, IVa or Va of the Periodic Table of the Elements,
A is a cation of group Ia, IIa, IIa of the Periodic Table of the Elements, a carbenium, oxonium or suffonium cation or a quaternary ammonium compound,
a is 2 or 3,
b is an integer from 2 to 5 and
c is an integer from 2 to 5.
The compounds of the present invention can be used together with metallocenes as catalyst systems in the polymerization of olefins, in particular the preparation of homopolymers or copolymers based on ethylene, propylene or norbornadiene, and also of functionalized olefins.